The overall goals of the Statistical Core are to: (1) To insure quality of data and its accessibility to project investigators; (2) To insure proper analysis of data for hypothesis testing and hypothesis generation; and (3) to insure that the data collected in each project and core are optimally utilized for both project specific and cross-project analyses. Specific aims of the Statistical Core are: (1) To insure a high quality of data for each of the projects and Cores; (2) To assist investigators in the analyses of the data on both a collaborative and consultive basis; (3) To facilitate the exchange of data and ideas among projects and cores; (4) To assist investigators in framing testable hypothesis and in generating hypothesis involving data from multiple projects; (5) To assist project investigators in conducting hypothesis testing using both cross-sectional and longitudinal data whenever possible; (6) To develop 'robust' cognitive test norms that are optimal for diagnosing AD (and other dementia) and identifying memory impairment in preclinical individuals; and (7) To develop methods to distinguish neuropsychological, neurologic, and neuropathologic deficits exhibited in early AD from changes which occur normal aging.